Veterinary Pathology. an acute, contagious disease occurring in horses and swine, characterized by fever, depression, and catarrhal inflammations of the eyes, nasal passages, and bronchi, and caused by a virus.

1743, borrowed during an outbreak of the disease in Europe, from Italian influenza "influenza, epidemic," originally "visitation, influence (of the stars)," from Medieval Latin influentia (see influence). Used in Italian for diseases since at least 1504 (cf. influenza di febbre scarlattina "scarlet fever") on notion of astral or occult influence. The 1743 outbreak began in Italy. Often applied since mid-19c. to severe colds.

influenza in·flu·en·za (ĭn'flōō-ěn'zə)n. An acute contagious viral infection, commonly occurring in epidemics or pandemics, and characterized by inflammation of the respiratory tract and by the sudden onset, fever, chills, muscular pain, headache, and severe prostration. Also called grippe.

(ĭn'fl-ěn'zə) A highly contagious infectious disease that is caused by any of various viruses of the family Orthomyxoviridae and is characterized by fever, respiratory symptoms, fatigue, and muscle pain. It commonly occurs in epidemics, one of which killed 20 million people between 1917 and 1919.

Our Living Language: Since ancient times, influenza has periodically swept the world. Until recently, people could not tell how this illness, which we call the flu, could spread so widely. Before people knew that organisms cause disease, they thought the stars influenced the spread of influenza. Influenza comes ultimately from the Latin word influentia, meaning "influence of the stars." Today, however, the stars are no longer blamed for the flu. Inhaling influenza viruses causes the spread of the illness.